Clothing Sizes

I've been noticing a trend - Libby's clothes are starting to get too tight. She is sadly wearing a sleeper that is for 3-6 months! How is that possible? She is growing up way too fast! I'm going to try to weigh her tomorrow on our own scale to see how much she has gained. I swear she is busting out of her Size 1 Diapers already that are supposed to go up to 14 lbs. I think she at least has to be 12 lbs by now. She's definitely growing, and I still have 0-3 month clothes that have not been worn! Yikes!